1. Field of the Invention
The present invention relates to a lock for raising and lowering boats as they pass from one level to another level in a canal, a river, or a dock, by means of lock chambers and lock gates.
2. Description of the Background Art
The Panama canal connecting the Atlantic and Pacific oceans is equipped with a multiple level lock.
Such a conventional lock in general operates as shown in FIGS. 1(A) to 1(E) sequentially.
First of all, the lock comprises a lower lock chamber 105 and an upper lock chamber 107 provided between a lower stream 101 and an upper stream 103, which are separated by a middle lock gate 111. The lower lock chamber 105 is separated from the lower stream 101 by a lower lock gate 109, and the upper lock chamber 107 is separated from the upper stream 103 by a front gate 113.
The lower stream 101 and the lower lock chamber 105 are connected at their bases by a lower pipe 115 equipped with a lower valve 117, the lower lock chamber 105 and the upper lock chamber 107 are connected at their bases by a middle pipe 119 equipped with a middle valve 121, and the upper stream 103 and the upper lock chamber 107 are connected at their bases by an upper pipe 123 equipped with an upper valve 125. Both of the lower lock chamber 105 and the upper lock chamber 107 are filled with appropriate amount of water initially.
Now, a boat K on the lower stream 101 can be raised to the upper stream 103 as follows.
First, as shown in FIG. 1(A), the lower lock gate 109 is opened, the boat K is lead from the lower stream 101 to the lower lock chamber 105, and then the lower lock gate 109 is closed. Here, the water corresponding to the displacement of the boat K is discharged from the lower lock chamber 105 into the lower stream 101.
Next, as shown in FIG. 1(B), the middle valve 121 is opened, the water is poured through the middle pipe 119 from the upper lock chamber 107 to the lower lock chamber 105 until the water level of the lower lock chamber 105 meets the water level of the upper lock chamber 107.
When the the water level of the lower lock chamber 105 meets the water level of the upper lock chamber 107, as shown in FIG. 1(C), the middle valve 121 is closed, the upper lock gate 111 is opened, the boat K is lead from the lower lock chamber 105 to the upper lock chamber 107, and then the upper lock gate 111 is closed.
Next, as shown in FIG. 1(D), the upper valve 125 is opened, the water is poured through the upper pipe 123 from the upper stream 103 to the upper lock chamber 107 until the water level of the upper lock chamber 107 reaches the water level of the upper stream 103.
When the the water level of the upper lock chamber 107 reaches the water level of the upper stream 103, as shown in FIG. 1(E), the upper valve 125 is closed, the front gate 113 is opened, the boat K is lead from the upper lock chamber 107 to the upper stream 103, and then the front gate 113 is closed. Here, the water corresponding to the displacement of the boat K flows from the upper stream 103 into the upper lock chamber 107. At the same time, the lower valve 117 is opened, and the water is discharged through the lower pipe 115 from the lower lock chamber 105 to the lower stream 101 such that the whole system returns to its initial state.
The boat K on the upper stream 103 can be lowered to the lower stream 101 by the reverse of the operation for raising the boat K just described.
Now, in the operation to raise the boat from the lower stream 101 to the upper stream 103 or the operation to lower the boat from the upper stream 103 to the lower stream 101 which uses the lock chambers such as the lower and upper lock chambers 105 and 107 above, there is a problem that in order to carry out these operations, an enormous amount of water is necessary.
In a case of Panama canal, the water resource is rather limited, and in the drier year in which the water level is low in the Gatun lake which is the upper stream for the Panama canal, limiting of the draft for the boat to pass through the canal is often necessary.
Thus, in order to cope with the increase of the passage through the canal, or in order to realize a larger lock capable of dealing with larger boats, it is indispensable to secure sufficient amount of water required for the operations at the lock, and it is preferable to reduce this amount as much as possible.
As a method of reducing the water consumption at the lock, there is a proposition to utilize horizontal water storage system for temporarily storing the water discharged from the lock chambers, so as to achieve the advantage of water saving similar to that obtainable by increasing the number of the lock chambers in the lock.
However, a number of such horizontal water storages are needed in this system to achieve a higher water consumption saving rate, and this makes the operation of the system very complicated.